Hi, does anyone know the correct size for the 2 ovals behind the front speaker in the HDTs. On the plans that I purchased from Decware which arn't the blue print ones, there are no measurements to the height or width. If you print the PDF file of that page at full size, the ovals measure 4" by 6", then if you drill half inch holes with centres on the oval line, the largest size of oval measures 4 and a half " by 6 and a half ". Are the ovals in the blue print plans a different size? The reason I ask is that in the paper written on ALT tuning kit it mentions that when fitting the foam above and below the main speaker you would need to cut some of the foam away from the top and bottom of each oval so that it does not protrude into the oval opening. With an oval cut at 4" by 6" this does not happen. I guess if the ovals are cut to the wrong size it could effect the sound. Any suggestions would be great.Stephen

Hi BobThanks for responding to my question. I still don't get these measurements. On the plans the size of the main driver cut out radius is 3-19/32 which is a diameter of 7-6/32. Now the size of the oval you say is 4" by 6", and by drilling the holes centered around oval at 1/2" you end up with a new oval at a maximum size of 4-1/2" by 6-1/2". So in my mind the oval size is still smaller than that of the main driver by 22/32", meaning it's not necessary to cut any of the foam that it says to do in the paper on HDT ALT Tuning. If the HDT ALT Tuning paper is correct in what it says about having to cut away some of the foam then the size of 4" x 6" for the oval is not correct. I would gather that the 4" bit of foam for above and below the main driver is placed with the foam starting at the edge of the cut out for the main driver. If I am missing something, I would love to know what it is?

Maybe your over thinking it, and maybe the paper isn't that clear on this.....You have to trim around all three openings, irregardless of the size of the holes. You could slide the foam down (below the driver) and there would be no need to cut the foam either. What the foam is trying to do here, is stop some of the back wave reflection off the two partitions immediately behind the driver. I think what might be confusing you is the fact that it states trimming around the "ovals" and not the driver. I haven't read the paper though, so I can't be sure.

Thanks again for your response. After reading your last answer you mention about adding foam directly behind the driver where the ovals are cut out to help reduce standing waves. In the paper written about the ALT tuning mods there is no mention of fitting foam directly behind the driver. In the ALT tuning paper it has 3 pieces of foam mentioned for the primary chamber, 1 is a triangle cut to fit under the top panel and 2 other pieces cut to a 4 inch wide strips as long as the 3 sides of the primary chamber, they are then fitted, 1 above the driver and 1 below the driver, but nothing directly behind the driver. So are all the new speakers sent from your factory fitted with foam that in fact covers the whole woodern surface in the primary chamber from about 4 inches below the driver right up to the top including under the top panel. If so this answers my question about the foam and I will apply the extra foam to my speakers. When purchasing the plans to make the HDT there is no mention of adding any foam at all, and only by coming across the ATL tuning paper which was left by another member on the forum, did I know about any of the foam along with the other tuning additions. Maybe the ALT tuning paper needs to be updated to include the extra foam that is not mentioned. Anyway hope I can rest in peace, thanks for your patience , I would just like to get it right.Regards Stephen

If you haven't built the speakers yet, you might not understand this right off....When you look at the surface that is remaining, after the ovals are cut away from the "X" partitions there isn't much directly behind the driver, with that said, if you look once built, if they aren't already, just sliding the foam about an 1" to an 1 1/2" up and down (depending on which side of the driver you talking about), you'll see a significant amount of surface covered with the foam, whats not covered is minimal and causes no ill effects.

HDT's leaving here, do not have all the back wall, directly behind the driver covered, (like described above) there really is no need for it.